Transcript Prezentace aplikace PowerPoint

Heavy flavor and dilepton
production in STAR experiment
Jaroslav Bielčík
for STAR collaboration
Czech Technical University
in Prague
Rencontres de Moriond QCD and High Energy Interactions
La Thuile, March 9-16, 2013
Outline
• Motivation.
• Open heavy flavor.
• J/y and Upsilon measurements.
• Dilepton production.
• Summary.
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Heavy quarks as a probe of
Radiative energy loss
QGP
• p+p data:
light
 baseline of heavy ion
measurements.  test of pQCD
calculations.
•
Due to their large mass heavy quarks
are primarily produced by gluon fusion
in early stage of collision.
 production rates calculable by pQCD.
M.Djordjevic PRL 94 (2004)
M. Gyulassy and Z. Lin, PRC 51, 2177 (1995)
Wicks et al, Nucl. Phys. A784 (2007) 426
• heavy ion data:
• Studying energy loss of heavy quarks.
 independent way to extract properties of
the medium.
• Dead cone effect.
[email protected]
3
The STAR Detector
•
VPD: minimum
bias trigger.
•
TPC: PID, tracking.
•
TOF: PID.
•
BEMC: PID, trigger.
Vertex Position Detector
4
D0 and D* pT spectra in p+p collisions
D0 yield scaled by
ND0/Ncc= 0.565
D* yield scaled by
ND*/Ncc= 0.224
•
FONLL upper band is
consistent with charm
spectra
STAR Preliminary
200GeV: Phys. Rev. D 86 (2012) 72013
FONLL: 200 GeV M. Cacciari, PRL 95 (2005) 122001
500 GeV Ramona Vogt µF = µR = mc, |y| < 1
.
d cc
dy
s  200 GeV
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 170  4559
b
y 0
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D0 spectra in Au+Au 200 GeV
•
•
•
Suppression at high pT in central and mid-central collisions.
Suppression at high pT in central collisions similar to light hadrons.
Enhancement at intermediate pT ~ models suggest radial flow of light quarks
coalescence with charm. P. Gossiaux: arXiv: 1207.5445
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Non-photonic Electron RAA in Au+Au 200 GeV
•
Strong suppression at high pT in
central collisions
•
D0, NPE results seems to be
consistent  kinematics smearing &
charm/bottom mixing
•
Uncertainty dominated by p+p result.
•
High quality p+p data from Run09 and
Run12 are on disk.
Non-photonic Electrons are
from semileptonic c and b decays
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Quarkonia states in A+A
Charmonia: J/y, Y’, cc
Bottomonia: (1S), (2S), (3S)
Key Idea: Quarkonia melt in the QG plasma due to color
screening of potential between heavy quarks
•
•
Suppression of states is determined by TC and their binding
energy
Lattice QCD: Evaluation of spectral functions  Tmelting
Sequential disappearance of states:
 Color screening  Deconfinement
 QCD thermometer  Properties of QGP
When do states really melt?
Tdiss(y’)  Tdiss(cc)< Tdiss((3S)) < Tdiss(J/y)  Tdiss((2S)) < Tdiss((1S))
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H. Satz, HP2006
J/y in Au+Au collisions
STAR high-pT : arxiv:1208.2736
Liu et al., PLB 678:72 (2009) and private comminication
Zhao et al., PRC 82,064905(2010) and private communication
• J/ψ suppression increases with collision centrality and decreases with pT
• Low-pT data agrees with two models including color screening and regeneration ef.
• At high pT Liu et al. model describes data reasonable well,
[email protected]
9
Models from M. Strickland and D. Bazow, arXiv:1112.2761v4
Nuclear modification factor of Upsilon
• Indications of suppression of (1S+2S+3S) getting stronger with centrality.
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ϒ RAA Comparison to models
• Incorporating lattice-based
potentials, including real and
imaginary parts
– A: Free energy
• Disfavored.
– B: Internal energy
• Consistent with data vs.
Npart
• Includes sequential melting
and feed-down contributions
– ~50% feed-down from cb.
M. Strickland, PRL 107, 132301 (2011).
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Dilepton Physics
Dileptons are excellent penetrating probes
– very low cross-section with QCD medium
– created throughout evolution of system
Chronological division:
• High Mass Range (HMR)
Mee > 3 GeV/c2
– primordial emission, Drell-Yan
– J/Ψ and ϒ suppression
• Intermediate Mass Range (IMR)
1.1 < Mee< 3 GeV/c2
– QGP thermal radiation
– heavy-flavor modification
• Low Mass Range (LMR)
Mee< 1.1 GeV/c2
– in-medium modification of vector mesons
– possible link to chiral symmetry
restoration
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dN/(dMdy) [(GeV/c2)-1]
Production in p+p at 200 GeV
10-1
Phys. Rev. C 86, 024906 (2012)
• Understand the p+p reference
h ® g ee
h’ ® g ee
r ® ee
p0 ® g ee & g ® ee
Cocktail simulation consistent with data
J/y ® ee
sum
cc ® ee (PYTHIA)
w ®ee & w ® p0ee
f ® ee & f ® hee
L. Ruan (STAR), Nucl. Phys. A855 (2011) 269
bb ® ee (PYTHIA)
p+p @ s = 200 GeV
10-4
Charm contribution dominates IMR
pe >0.2 GeV/c, |he|<1
– consistent with STAR charm crosssection
T
Adams et al (STAR), Phys. Rev. Lett. 94 (2005) 062301
Data/Cocktail
10-7
Uncertainties:
2
0
0
1
Mee (GeV/c2)
2
3
•
•
•
•
vertical bars: statistical
boxes: systematic
grey band: cocktail simulation systematic
not shown: 11% normalization
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Production in Au+Au 200 GeV
Low Mass:
STAR Preliminary
• enhancement
when compared to
cocktail (w/o ρ meson)
little centrality
dependence
Intermediate Mass:
STAR Preliminary
cocktail “overshoots”
data in central
collisions
but, consistent within
errors
modification of charm?
difficult to disentangle (modified) charm from thermal QGP contributions
 future detector upgrades required HFT+MTD
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Dielectron Production at lower √sNN
Beam Energy Scan Dielectrons 2010 – 2011:
Au+Au at 62.4, 39, and 19.6 GeV
STAR data samples: 55M, 99M, and 34M min-bias events
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Compare to Theory: in-medium ρ
• Robust theoretical description top RHIC down to SPS energies
•
– calculations by Ralf Rapp (priv. comm.)
– black curve: cocktail + in-medium ρ
Measurements consistent with in-medium ρ broadening
– expected to depend on total baryon density
– tool to look for chiral symmetry restoration
STAR
Preliminary
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Summary and Outlook
• Large suppression of heavy quark production at high-pT in D0 and
non-photonic electrons measurements in 200 GeV central Au+Au collisions.
Similar to light quarks.
• J/ψ suppression increases with collision centrality and decreases with pT.
• Increasing of ϒ suppression vs. centrality.
RAA consistent with suppression of feed down from excited states only (~50%).
• Dielectron measurement in p+p 200 GeV.
Cocktail describes the data well.
• Dielectron measurement in Au+Au 19.6 – 200 GeV.
Low mass enhancement down to low (SPS) energies observed.
Consistent with in-medium ρ broadening.
• Heavy flavor tracker and Muon telescope detector upgrades.
Significant improvement of heavy flavor, quarkonium and dilepton measurements.
[email protected]
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Heavy Flavor Tracker
HFT
SSD
IST
PXL
Inner Field Cage
Outer Field Cage
TPC
Volume
Detector
Radius Hit Resolution Radiation
(cm) R/ - Z (m - m) length
SSD
22
20 / 740
1% X0
IST
14
170 / 1800
<1.5% X0
8
12 / 12
~0.4% X0
2.5
12 / 12
~0.4% X0
PIXEL
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Physics projections – punchline for Y13,14
RCP=a*N10%/N(6080)%
Assuming D0 Rcp distribution as
charged hadron.
Assuming D0 v2 distribution from
quark coalescence.
500M Au+Au m.b. events at 200 GeV.
500M Au+Au m.b. events at 200
GeV.
- Charm RAA
Energy loss mechanism!
Color charge effect!
Interaction with QCD matter!
- Charm v2
Medium thermalization degree
Drag coefficients!
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Future: ϒ via STAR MTD
MTD (MRPC)
•
A detector with long-MRPCs
– Covers the whole iron bars and leave the gaps in between uncovered.
– Acceptance: 45% at | |<0.5
•
•
– 118 modules, 1416 readout strips, 2832 readout channels
Long-MRPC detector technology, electronics same as used in STAR-TOF
Run 2012 -- 10%; 2013 – 60%+; 2014 – 100%: ϒ via +20
STAR Dileptons: Present & Future
• 2009 – 2011
– TPC + TOF + EMC
• dielectron continuum
• dielectron spectra, and v2 (pT)
– vector meson in-medium
modifications
– LMR enhancement
– modification in IMR?
• 2014 and beyond
– TPC + TOF + EMC + MTD + HFT
• dimuon continuum
• e-μ spectra and v2
– LMR: vector meson in-medium
modifications
– IMR: measure thermal QGP
radiation
• 2012-2013
– TPC + TOF + EMC + MTD
(partial)
• e-μ measurements
– IMR: Improve our understanding
of thermal QGP radiation
– LMR: vector meson in-medium
modifications
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D0 and D* pT spectra in p+p 200 GeV
Phys. Rev. D 86 (2012) 072013.
•
The charm cross section
at mid-rapidity:
ds
dy
•
pp
= 170 ± 45+38
-59 m b
y=0
Upper limit of FONLL
describes the data well
Fixed-Order Next-to-Leading Logarithm: M. Cacciari, PRL 95 (2005) 122001.
22
D0 and D* pT spectra in p+p collisions
D0 yield scaled by
ND0/Ncc= 0.565[1]
D* yield scaled by
ND*/Ncc= 0.224[1]
STAR preliminary
[1] C. Amsler et al.
(Particle Data Group), PLB
667 (2008) 1.
[2] FONLL calculation:
Ramona Vogt
µF = µR = mc, |y| < 1
FONLL upper band consistent with
500GeV (200GeV) charm spectra.
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 in Au+Au 200 GeV, Centrality
STAR
Preliminary
STAR
Preliminary
Peripheral
14/Nov/12
STAR
Preliminary
Central
Manuel Calderón de la Barca
Sánchez
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 in Au+Au 200 GeV
•
•
 has negligible recombination; smaller co-mover absorption
Raw yield of e+e- with |y|<0.5 = 197 ± 36
Advantage:
∫L dt ≈ 1400 µb-1
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Dileptons Au+Au theory comparison
• STAR central 200 GeV Au+Au
• hadronic cocktail (STAR)
Ralf Rapp (priv. comm.)
R. Rapp, Phys.Rev. C 63 (2001) 054907
R. Rapp & J. Wambach, EPJ A 6 (1999) 415
Complete evolution (QGP+HG)
cocktail + HG + QGP:
Rapp, Wambach, van Hees
arXiv:0901.3289
 Agreement w/in uncertainties
 hadronic phase: ρ “melts” when
extrapolated close to phase transition
boundary
• total baryon density plays the essential role
 top-down extrapolated QGP rate closely
coincides with bottom-up extrapolated
hadronic rates
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